This invention relates to a photothermographic material capable of forming an image through heat development and more particularly, to a photothermographic material having a photosensitive layer firmly adhered to a support.
There are known many photosensitive materials comprising a photosensitive layer on a support which are exposed imagewise to form images. Among them, a process of forming an image through heat development is known as an environmentally friendly system capable of simplifying image forming means.
The process of forming an image through heat development is disclosed, for example, in U.S. Pat. Nos. 3,152,904 and 3,457,075, and D. Morgan and B. Shely, "Thermally Processed Silver Systems" in "Imaging Processes and Materials," Neblette, 8th Ed., Sturge, V. Walworth and A. Shepp Ed., page 2, 1969. These photosensitive materials generally contain a reducible non-photosensitive silver source (e.g., organic silver salt), a catalytic amount of a photocatalyst (e.g., silver halide), and a reducing agent for silver, typically dispersed in an (organic) binder matrix. Photosensitive materials are stable at room temperature. When they are heated at an elevated temperature (e.g., 80.degree. C. or higher) after exposure, a redox reaction takes place between the reducible silver source (functioning as an oxidizing agent) and the reducing agent to form silver. This redox reaction is promoted by the catalysis of a latent image produced by exposure. Silver formed by reaction of the organic silver salt in exposed regions provides black images in contrast to unexposed regions, forming an image.
Such photosensitive material capable of forming an image through heat development, generally referred to as photothermographic material, can satisfy the recently increasing demand for simpler processing and environmental protection.
In the prior art manufacture of photothermographic material, photosensitive layers were formed by applying a coating solution of effective components and a binder in an organic solvent and drying the coating. For example, U.S. Pat. No. 5,415,993 discloses a solution of polyvinyl butyral binder in a solvent mixture of toluene and methyl ethyl ketone. The use of organic solvents, however, is undesirable from the environmental protection and safety standpoints. Then techniques of forming photosensitive layers using aqueous solvents were devised. Such techniques of forming photosensitive layers using aqueous solvents are disclosed in, for example, JP-A 116114/1978, 151138/1975, and 28737/1983 which use gelatin, polyvinyl alcohol and polyvinyl acetal as the binder, respectively. These systems, however, have the drawback that the photosensitive layer forms an insufficient bond to the support. There is a desire to have a technique of manufacturing a photothermographic material devoid of such drawbacks using a coating solution of an aqueous solvent.